1. Field of the Invention
This invention relates to a strain gauge having alternate sections of concave and convex, concave and flat or square wave shapes that can be stretched with very little force and to a method of making such a strain gauge.
2. Description of the Prior Art
Heretofore, most strain gauges were of the type adapted to be bonded to a substrate to provide a measurement of strain of an object. In the measurement of dynamic movement, such as abdominal movement of an infant to monitor respiration, such a strain gauge would be unsatisfactory in that it would restrict movement and interfere with the breathing process. One strain gauge which has been used for this purpose in the past, is the mercury strain gauge. This comprises a flexible thin wall rubber tube filled with a conductive medium such as mercury and having electrical contacts at opposite ends. As the tube is stretched, the body of mercury becomes longer and thinner and the resistance through the gauge is increased. This type of gauge, in this application, has several drawbacks. First, as oxygen diffuses through the rubber tube, the mercury can oxidize and provide intermittent electrical contact. Also, because of the toxic nature of mercury, use of the gauge is limited to a carefully watched clinical setting and can not be used at home. Other home use infant respiratory monitors are subject to false readings and at times can be unreliable.